Potentiometer wiper contact assembly



R. D. FERRARI POTENTIOMETER WIPER CONTACT ASSEMBLY Jan. 29, 1963 Filed March 8, 1961 .Jgoom o D. .Fi'R/M 5 Wm am United States Patent Qfhce 3,675,162 POTENTIIOMEIER WIPER CONTACT AlSEll EBLY Rodolfo 13. Ferrari, West Covina, Caiif., assignor to Spectrol Electronics Corporation, San Gabriel, Calih, a corporation of Delaware Filed Mar. 8, 1961, Scr. No. 94,218 3 'laims. (Cl. 338--167) The present invention relates to a variable electrical device and particularly to an apparatus wherein an impedance element may be variously engaged by a relativelymovable contact to provide a variable impedance.

As a result of widespread developments in automatic control apparatus, and other complex electrical systems, considerable demand exists for potentiometers as a means of providing a variable resistance impedance. One common basic form of potentiometer employs a resistance element which may be connected across a source of electrical potential so that each point along a contact path on the resistance element provides a different voltage. Various wiper arrangements are then used to contact the resistance element at different points under the control of a rotative shaft or other mechanical means.

In many applications of potentiometers good electrical contact between the wiper and the resistance element is exceedingly important. It is also important that the wiper make a smooth transition between voltage levels on the resistance element, to avoid the formation of noise signals. That is, if the wiper intermittently contacts the resistance element, or skips from one contact point to another, spurious signals are introduced into the related electrical system which may cause a malfunction.

One manner of assuring continuous contact between the Wiper and the resistance element in a potentiometer is to providea substantial spring force in the wiper so that it forcefully engages the resistance element. As a result, the wiper maintains continuous contact with the resistance element and generally avoids the formation of spurious signals. However, as a result of the force between these elements, an increased friction force results which opposes the movement of the wiper and reduces the useful life of the potentiometer by increasing Wear between the elements. Therefore, contact force in prior potentiometers has generally been determined by a compromise between useful life and continuity of contact. As a result, a need exists for an improved wiper apparatus which provides good electrical contact with the resistance element, while employing a minimal force between the wiper and the resistance element.

In general, the present invention comprises a variable electromechanical apparatus incorporating an impedance element having a contact path, and a wiper apparatus which may be positioned to engage the impedance element at different locations on the contact path. The Wiper apparatus includes a plurality of circular convolutions which are individually afiixcd to the wiper support apparatus so as to be resiliently deformable and thereby provide continuous contact with the impedance element.

An object of the present invention is to provide an improved variable-impedance electrical apparatus.

Another object of the present invention is to provide a potentiometer capable of long life and reliable operation.

Still another object of the present invention is to provide a potentiometer capable of reliable operation with reduced contact pressure.

A further object of the present invention is to provide a potentiometer structure in which optimum materials may be economically employed.

Still a further object of the present invention is to provide a wiper contact for use in a variable-impedance device, which contact includes a plurality of circular con- 3,975,162 Patented Jan. 29, 1.1 253 in volutions that are resiliently deformable to reliable contact an impedance element.

The structure of the invention, and the objects thereof will become apparent from a consideration of the following description taken in conjunction with the drawing, in which:

FIG. 1 is a sectionalized perspective view of an apparatus constructed in accordance with the present invention;

FIG. 2 is an enlarged line 2-2 of FIG. 1; and

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.

Referring initially to FIG. 1, there is shown a housing 10 containing a resistance element or C-shaped coil 12 concentrically mounted therein. The coil 12 may be variously engaged along a contact path by a rotativelymounted carriage or wiper assembly 14, to tap various voltages from the coil 12. The actual contact between the coil 12 and the wiper assembly 14 is made by a plurality of circular contact fingers 16 which may compartial sectional view taken along prise convolutions of a resiliently-deformable wire helix,

each of which is rigidly affixed Considering the apparatus in greater detail, the housing 10 includes a hollow cylinder 1% closed at one end by an integral end plate 29 to form a cup. The other end of the cylinder is closed by a circular cap 22 containing a peripheral annular groove 24 which receives studs 25 that pass through the edge of the cylinder 18 are are threadably afiixed therein. The integral cylinder 18 and end plate 26, along with the cap 22 may be formed of tempered aluminum and anodized for resistance to corrosion.

An insulation support strip 28 is concentrically mounted in the hollow cylinder 18 substantially midway between the end plate 20 and the cap 22, and abuts against an inside shoulder 23 formed in the cylinder 18. The resistance coil 12 is affixed to the strip 28 and extends about the interior of the cylinder 13 to provide a curved contact path along its inside surface. The coil 12 may comprise a precision wire-wound resistance element or various other impedance elements.

The coil 12 and the wiper assembly 14 are adapted to be connected to an electrical circuit through terminals 39, 32 and 34. These terminals extend radially through the hollow cylinder 13 and are aflixed therein by glass, mounting grommets 3d, 38 and 4d. The coil 12 is connected be tween the terminals 30 and 32 by lead wires 42 and 44, while terminal 34 is connected to the Wiper assembly 14-.

The wiper assembly 14 includes a slip ring 5 which is affixed to a shaft is concentrically mounted within the cylinder 13 and journalled into bearings 43 and 50, that are concentrically mounted in the cap 22 and the end plate 2%) respectively. The shaft 46 also carries spacer 51 which holds the slip-ring together with a contact to the wiper assembly 14.

r arm 54 to form an annular groove which receives a slipring brush 56 extending from the terminal 34.

The contact arm 54 extends radially from the shaft 46 and supports a leaf sprin afiixed at its end, which in turn carries the fingers 16. Considering the structure or" the leaf spring and the fingers 15 in greater detail, reference will now be had to FIGS. 2 and 3.

In the enlarged views of FIGS. 2 and 3, the coil 12 may be seen to consist of an annular base 57 which carries a wire 58 spirally wound thereon. The composite irregular inner surface of the coil 12 then provides the contact path along which the fingers 16 are carried on the leaf-spring 55. The fingers 16 may comprise a spirally Wound section of metal wire, e.g. precious metal, each circular convolution of which is individually afiixed to the leaf-spring 55 as by a weld at}, with no interior interference.

One manner of forming the fingers 18 is to closely ment provides some twelve convolutions of the helix. The

individual convolutions of the helix are next soft-soldered or tap-welded at the centerline to the leaf spring 55 to provide the uniform, independent contact fingers which engage the coil 12 in-space quadrature to the leaf spring As a result of this structure separate optimum materials may be employed to form the leaf-spring 55 and the fingers 16 so as to utilize materials providing the best characteristics for each of these elements. One successful embodiment of the present invention utilizes beryllium copper for the leaf spring 55 and precious metal for the fingers 16. In such a combination, the amount of-precious metal is small yet exceedingly good electrical characteristics are provided at theactual point of contact, and the leaf spring is reliable.

In the operation of a potentiometer incorporating the' present invention, the leaf-spring 55 is adjusted to provide sufficient tension to resiliently deform and thereby off-set certain of the fingers 16 from a uniform contact edge to engage the coil 16 is invariably in electrical contact with the coil 12.

Referring now to FIG. 1, it may be seen that'as the shaft 46 is revolved, the arm 54 carrying theleaf-spring 55 is moved in a circular path causing the fingers 16 to variously engage the coil 12. At least one of the-fingers 12 will invariably establish good electrical contact with the coil 12; however, due to the size of the wire forming the fingers 12, the area-of-contact is quite small andthe area of wear is similarly small. As one of the fingers invariably contacts the coil 12, the contact force or pressure need not be particularly large with the result thatwear between the fingers 16 and the coil 12 is reduced and the force required to revolve the shaft 46 may be very small.

An important feature of the present invention in addition to the aspects considered above, resides in the fact that inspite'of small contact pressure and area, one of the fingers will continuously contact the coil 12 so as to minimize if not completely avoid the formation of spurious signals' which result from interrupting the contact between a wiper apparatus and the resistance element.

Although these and other important features of the present invention are apparent in the described embodiment of the invention, it will also be. apparent that the present invention provides an apparatus capable of many variations and modifications, consequently the present invention is not to be limited to a particular arrangement to the Width of the 12. As a result, at least one of the fingers 4 as herein shown and described except as defined by the appended claims.

What is claimed is:

l. A variable impedance apparatus for use in an electrical circuit, comprising: an impedance element having an irregular contact path along which said impedance element may be electrically contacted; terminal means electrically connected to the ends of said element; flexible contact support means; contact means including a plurality of circular convolutions, each of said circular convolutions being individually affixed to said contact support means whereby said contact means engages said irregular contact path; carriage means for moving said contact support means whereby to move said contact means contact path; and couplingmeans for connecting said impedance element and said contact support means to said electrical circuit.

2. A variable impedanceapparatus for use inan electrical circuit,- comprising: an elongate resistance element having an irregular-surface contact path along which said impedance element may be contacted; an elongate leaf spring; contact means precious'metal helix, one endof said leaf spring by each convolution thereof being individually attached to said one end whereby said contact path engages certain of said convolutions in space quadrature to said leaf spring to resiliently offset said certain convolutions; carriage means for moving said leaf spring whereby to move said contact means along saidcontact path; and coupling means for connecting. said resistance element and said contact means to said electrical circuit.

3. A variable impedance apparatus for use in an electrical circuit, comprising: an elongate resistance element including a resistance wire coiled about the axis of saidelement to provide anirregular contact path parallel to theaxis of said element and with an irregular surface; an elongate leaf spring formed of non-precious metal;

contact means-including plural convolutions of a precious- References Cited in the file of this patent UNITED STATES PATENTS 2,975,389 Karg Mar. 14, 1961 along said including plural convolutions of asaid contact 1 means being afiixed at- Berthiez July 19, 1949' 

3. A VARIABLE IMPEDANCE APPARATUS FOR USE IN AN ELECTRICAL CIRCUIT, COMPRISING: AN ELONGATE RESISTANCE ELEMENT INCLUDING A RESISTANCE WIRE COILED ABOUT THE AXIS OF SAID ELEMENT TO PROVIDE AN IRREGULAR CONTACT PATH PARALLEL TO THE AXIS OF SAID ELEMENT AND WITH AN IRREGULAR SURFACE; AN ELONGATE LEAF SPRING FORMED OF NON-PRECIOUS METAL; CONTACT MEANS INCLUDING PLURAL CONVOLUTIONS OF A PRECIOUS METAL HELIX, SAID CONTACT MEANS BEING AFFIXED AT ONE END OF SAID LEAF SPRING BY EACH CONVOLUTION THEREOF BEING INDIVIDUALLY ATTACHED AT A SIMILAR RADIAL LOCATION TO SAID ONE END OF SAID LEAF SPRING WHEREBY SAID CONTACT PATH RECEIVES CERTAIN OF SAID CONVOLUTIONS IN SPACE QUADRATURE TO SAID LEAF SPRING TO RESILIENTLY OFFSET SAID CERTAIN CONVOLUTIONS; CARRIAGE MEANS FOR MOVING SAID LEAF SPRING WHEREBY TO MOVE SAID CONTACT MEANS ALONG SAID CONTACT PATH; AND COUPLING MEANS FOR CONNECTING SAID RESISTANCE ELEMENT AND SAID CONTACT MEANS TO SAID ELECTRICAL CIRCUIT. 